Cyanid process of working gold, silver, or other ores.



No. 705,998. Patented July 29,- |992. H. H. oFFxcEH, J. w. NEILL, J. H.BUHFEIHD 9 F; H. oFncEn. GYANID PROCESS OF WORKING 60ML-SILVER, OB OTHEROBES.

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UNITED. STATES PATENT OFFICE.

ROBERT H. OFFICER, JAMES W. NEILL, JOACHIM H. BURFEIND, AND FRANK H.OFFICER, OF SALT LAKE CITY, UTAH.

CYANID PROCESS OF WORKING GOLD, SILVER, `OR OTHER ORES.

SPECIFICATION forming part of Letters Patent No. 705,698, dated July 29,1902. Application ledJ'une 10, 1901. Serial No. 63,859. (No specimens.)

T0 all wil/071@ it may concern:

Be it known that we, ROBERT H. OFFICER, JAMES W. NEILL, JOACHIM H.BURFEIND, and FRANK H. OFFICER, citizens of the United States,and'residents of Salt Lake City, in the p county of Salt Lake and Stateof Utah, have for instance, cyanid of potash-is used as a` solvent forrecovering gold, silver, or other precious metal from ores, tailings,slimes, or other material; and its object is, generally speaking, tocheapen the process by reducing the loss of valuable solvent, to lessenthe time of the operation, to avoid danger to Workmen, and to secureother advantages which will be obvious to those skilled in the art fromthe subjoined description of our process.

Our invention is designed principally for use in those processes whereina charge containing the cyanid is agitated by air or other gas forcedinto or through the charge; vbut is also applicable to other processeswherein hydrocyanic-acid gas is freed or released during the process oftreating the material contained in a suitable treating tank or vat.

Briefly stated, our invention consists in conveying the hydrocyanic-acidgas released in the treating-tank to a suitable regenerator-tank, Whereit is brought into contact With a suitable solution of caustic soda,caustic potash, or other salt suitable for producing a cyanid salt.

When ou'Il invention is carried out in` connection with the process ofagitating the material in the treating-tank by air, We notonlyareenabled to recover the hydrocyanic acid in a useful form, but by usingthe air over and over again We avoid the action ofv carbonic acid andoxygen upon the cyanid in the treating-tank.

Our `invention consists also in other improvements hereinafter moreparticularly described and then specified in the claims..

Our invention is useful not only in the treatment of ores, tailings, orslimes for theV purpose of recovering gold` or silver by the receive thecharge which is to undergo treatment. The tank or vat may be of anydesired form, but is preferably constructed to permit the charge to bereadily agitated by a stream of air or other gas introduced into thecharge under pressure in such a way as to circulate the same and tothereby bring all parts of the metal-bearing material into con- 7o tactWith the solvent. Preferably, therefore, We use a `tank having a conicalbottom, as shown, and provided with means for introducing air or gasunder pressure in a stream directed downwardly or outwardly at the apexof the conical bottom, so as to produce a circulation of the pulp upwardalong the sides of the tank and then downward around the center.

1l indicates a suitable pipe whose outletis 8o located as described andwhich leads from any suitable receiver or source of air or gas underpressure, such as indicated at 12.

l is a cock for controlling the iioW of the gas or air through thepipell.

14 is a dischargepipe connected With the bottom of the tank forconveying the pulp to any suitable filter-press, (indicated in outlineat 15,).and 13 is a pipe connected with any suitable source of airor gasunder pressure, 9o preferably the receiver 12,' and serving to introduceair or gas under pressure into the discharge-passage from the tank.

Suitable valves l, 2, and (i are located, as shown, to control the lioWof the air or gas and of the liquid. By opening valves 2 and G the pulpis permitted to flow to the filterpress, and at the same time by openingvalve l gas may be directed into the discharge-pipe in any desiredquantity to act as an injector' Ico to help to force the pulp throughthe outletpipe 14 to the filter-press or into anyT other vessel. Byclosing valve 6 and causing the air passing through pipe 13 to beintroduced 'forcibly upward into the bottom'of the tank sedimentcollecting at that point may be removed should it collect so as to clogthe bottom of the vat.

Tank 10 is closed at its top', but is provided with a suitablecharge-hole at 3, that may be sealed in any proper manner, and with anair or gas outlet 16, controlled by a suitable valve 5. Another pipe 17leads from any suitable tank containing a solution of the cyanid orother substance used in treating the ore, slimes, tailings,concentrates, or other metalbearing material.

18 is a suitable regenerator-tank, which in carrying on our process isto be charged with a solution of caustic soda, caustic potash, causticlime, or any other caustic alkali or alkaline earth adapted to unitewith or absorb hydrocyanic acid, and thus produce the soluble simplecyanid adapted to act as a solvent for gold, silver, or other metalcontained in the material which is to be treated in the tank or vat 10.The tank 18 is preferably located at a higher level than the tank 10, sothat the solution of cyanid salt generated therein may flow by gravitythrough pipe 17 to the tank or vat where it is to be employed as asolvent. A suitable valve 7 may be located in the passage or pipe 17 tocontrol the iiow of the solution from the tank 18. The tank 18 is closedat its top, but is provided witha suitable charge hole or opening forthe caustic liquid employed in making the generating solution. It isalso provided with an inlet-pipe 19, connected with the pipe 16 andadapted to introduce the air or gas collected at the top of the tank 10into the solution in tank 18, near the bottom thereof, whence it passesupward through the solution, and nally escapes by the pipe or passage20. A number of screens 21, provided with small openings, may be placedin the tank to break up the flow of the gas and bring about a moreintimate contact of the solution therewith.

22 typiiies a compressor of any suitable construction Which receives theair or gas de livered from the regenerator after it has parted with itsvaluable constituents and compresses the same into the tank or receiver12, from which it may be delivered to the treating tank or vat, asalready described.

23 is a suitable in-take controlled by a valve, as indicated, by whichair may be taken directly into the compressor for the purpose ofproviding the initial charge of air or gas used in the operation, or forthe purpose of introducing air together With the gas received throughpipe 2O into the compressor, should it be so desired at any time duringthe operation. Ordinarily the in-take 23 is closed and the operation ofthe compressor 22 is obviously to produce circulation of the air orother gas or gaseous mixture through the dissolving-tank 10 andregenerator-tank 18 in a continuous circulation over and over.

The apparatus so fardescribed is the preferred and desirable form ofapparatus suit- 'able for carrying on the process which We vis used toagitate the charge in the treating tank or vat.

In practicing our invention in connection with ores, tailings, slimes,or other material free from ingredients which would tend to consume ordecompose the cyanid used as a solvent to no useful purpose, the processWill be conducted as follows: The cyanid solution of the requiredstrength and volume, depending upon the nature of the material to betreated as ascertained by a preliminary test, is introduced into thetank 10, and then, by preference, the air or gas is introduced into thetank by opening valve 4 and, if desired, valves 1 and 2 also, the valve6 being at such time closed. By this means the solution is agitated, andinto the agitated solution is charged the material to be treated, which,as well understood in the art, should be of the properiineness. By thismeans the materiales soon as it is introduced through the opening 3 isat once mixed thoroughly With the cyanid solution. The charge-opening 3is then tightly closed and the valve 5, which at the preliminary stageshould be closed, is then opened and the air or gas after circulatingthrough the charge is permitted to pass, together with any hydrocyanicacid set free in the solution, to the regenerator-tank 18, Where itcomes into contact With the caustic solution and in order to escape hasto pass upward through the same and thence is carried by the pipe 2Oback to the receiver 12 by the action of the compressor. By this meansthe hydrocyanic acid freed from the tank 10 and which may exist in aconsiderable amount when alarge amount of air is used for agitation willbe absorbed in the caustic solution, and thus produce the cyanid salt,which is useful as a solvent, in the tank 10. By using the air or gasafter it has passed through the regenerator-tank again for agitating thesolution we avoid the action of the carbonic acid and oxygen, Whosepresence in t-he air brings about the liberation or freeing of thehydrocyanic-acid gas in the solution, and at the same time recovery ofsuch of the hydrocyanic gas as maybe freed in the form in which it maybe used again as a solvent. As will be obvious the expense of this ispractically only the cost of the caustic lime, soda, or other materialthat may be required in the regenerator-tank. While the operation iscarried on in this manner there Will be in the dissolving tank or vat apressure which maybe regulated practically by the height of the solutionin the regenerator, and this pressure Will much accelerate the action inthe dissolving-tank. The operation having been carried on until the pre-IOO IIO

IZO

cious metals have been dissolved in the charge,

the flow of the air or gas through the solution is stopped byclosing-valve 5, and valve G is opened so that the pulp may be allowedto ow to the filter-press, carrying the solution containing the preciousmetal with it, where the solution is freed from the gangue and is thenin the usual manner conducted to the precipitating apparatus, afterwhich it may be used again on a fresh charge of material or until itbecomes foul or inert. Vhile the pulp is passing to the press itsmovement may be accelerated, if desired, by allowing the valve 1 to4remain partially open. If desired, the valve 1 may be kept closed duringthe operation of treating the material and only opened in oase the tankshould become clogged at the outlet or apex. After the charge is in thelter-press the air-pressure may be raised, so as to press out all thesolution possible, and then in order to displace the small amount ofvaluable solution ieftin the press-cakes water may be forced throughthem while yet in the press to replace the remainder of the valuablesolution, and the cleansingwater may be also carried to theprecipitating apparatus,as well understood in the art. The press is thenopened andthe valueless gangue removed in any desired manner.

The solution produced in the tank 1S by the hydrocyanic acid recoveredtherein may, as occasion requires, be introduced into the tank 10through pipe 17 or otherwise. By this process we not only secure avaluable solvent from the hydrocyanic acid released or disengaged inthetreatingtank or vat, but also remove danger'to workmen met in alloperations wherehydrocyanic acid is set free and allowed to escape tothe atmosphere.

In case the ores, tailings, slimes, or other `materials are of an acidnature or contain earths--the material may be given a preliminarytreatment in the dissolving vessel or in any other vesselby treating itwith a solution containing some caustic alkali or alkaline earth,usually caustic lime or caustic soda. In this preliminary treatment thecharge may be agitated, as already described, until the objectionableelements have been removed or changed to inert ones. Thus, for instance,if the material contains ferrous sulfate (FeSO4) and the solutioncontains caustic lime and the reaction is as follows:

not reduced the cyanid-consuming quality of the ore; but ferrous hydratein contact with air is quickly changed to ferrie hydrate, and thislatter compound is inert with soluble cyanids. Whentheobjectionableingredient to be treated has thus been changed or removed,`then we simply add the required amount of the cyanid solvent to thecharge, and the treatment already described is carried on.

When ores containing copper are treated by the cyanid method, thesolutions soon become charged with copper, which makes them inactive andsluggish. In the old method attempts are made to free them from thiscopper by precipitating it on zinc. This is a tedious and expensiveoperation, one so much so that at most works where such ores are treatedthe foul solutions (solutions containing copper) are run to Waste fromtime to time. The loss of precious metals and cyanid when such foulsolutions are run to Waste is large. In this case the foulsolution ischargedinto the dissolvingtank or vat and is then slightly acidifiedbest and most inexpensively by the SO2 gas, or, if desired, by sulfuricacid. The charge-hole is then closed air-tight and the solution agitatedby the compressed air introduced through the pipe 11 or pipe 13, orboth, and the air leaving the dissolving-tank charged withhydrocyanic-acid gas is carried to the regenerator, where it comes intocontact with the caustic solution, as already described, and thehydrocyanic acid is absorbed with avidity by the caustic solution, thereaction being as follows:

After the copper, gold', and silver have been precipitated from thesolution by the sulfuric acid and the hydrocyanic acid set free has beendriven out the entire contents of the dissolving vessel are passed intothe filterpress and the precipitate washed repeatedly and thoroughly, soas to free it from the adhering solution. The precipitate (cuprous IOOIIO

auro-cyanid or the respective silver salt) is l then removed from thepress andtreated like other products from cyanid Works or sold torefiners.

The arrangement of air or gas pipes 11 and 13, whereby the air or gasunder pressure may be introduced into the tank, as hereinafterdescribed, gives us this advantage: that by opening the Valve 4c theliquid can be stirred or agitated, while by opening the valves 1 and 2the heavier portions of the charge, which tend to settle into the outletof the tank leading to the filter-press, may be kept :from lodging insaid outlet, thus keeping the pipe free, so that when the pipe 6 `isopen the charge will fall readily into the lter-press and acomparatively small pressure will be required to effect its movement.This is a very greatimprovement upon the devices heretofore employed,since if no means be used to keep the outlet free or to dislodge anyaccumulation in the outlet an air-pressure even as high as two hundredpounds Will not serve to dislodge the accumulation of heavier materialwhich may exist at the outlet after the treatment or agitation of it byair through the pipe 11 alone. By this improvement We eectually preventclogging, thus saving time and annoyance in that part of the operationwhich involves the removal of the pulp from the treating-tank to thefilter-press.

Inasmuch as carbonio acid contained in the air or gas used to agitatethe charge in cyaniding a gold or silver ore Will always decompose moreor less of the solvent for the gold and also in the preliminarytreatment of the ore by caustic alkali or alkaline earth will convertpart of the caustic to carbonate, and thus render it useless for thepurposes for which it Was introduced into the charge, it is desirable tohave the air used in stirring the charge free fromcarbonic-acid gas.This can easily and cheaply be effected by placing between thecompressor and the treating-tank a vessel similar to theregenerating-tank and charging it with a material which will absorbcarbonic acid, such as milk of lime or a solution of a caustic alkali oralkaline earth. The air or gas passing through this will give up itscarbonic acid and enter the charge of ore free from this deleterioussubstance. Such a vessel is indicated in outline at 40.

In the appended claims the term gas is to be taken as including airunless otherwise specified.

The apparatus herein described as employed in carrying out our inventionis not claimed herein, since it forms the subject of claims in anotherapplication for patent filed by us December 24, 1901, Serial No. 87,060.

We claim as our inventionl. The herein-described improvement in thecyanid process of recovering precious metals from ores, slimes, tailingsor concentrates, consisting in treating the ore, slime, tailings orconcentrates with a suitable cyanogen compound and passing thehydrocyanic-acid gas set free by such treatment through a regeneratingcaustic solution, as and for the purpose described.

2. The herein-described improvement in treating the foul or spentsolution resulting from the cyanid process of extracting gold and silverfrom ores, consisting in passing sulfurous-acid gas through saidsolution and then filtering and Washing to recover the metalsprecipitated by the acidification.

' 3. The herein-described improvement in treating ores by the cyanidprocess consisting in agitating the pulp containing the cyanid solutionby a suitable gas under pressure, passing the gas and thehydrocyanic-acid gas liberated from the solution through a regeneratingsolution and using the gas after passing through said regeneratingsolution to agitate a fresh quantity of pulp.

Signed at Salt Lake City, in the county of Salt Lake and State of Utah,this 25th day of May, A. D. 1901.

ROBERT H. OFFICER. JAMES W. NEILL. JOACHIM II. BURFEIND. FRANK II.OFFICER. Witnesses:

W. A. BLACK, M. J. MooNEY.

